Decavalent IgM antibodies display measurable binding avidity to antigens, even though binding affinity may be low. The multivalent structure of pentameric IgM provides the potential for cross-linking cell surface targets, endowing the soluble antibodies with biological potential not normally associated with immune function.
Dendritic cells (DC) are efficient antigen-presenting cells (APC). These cells express class I and class II major histocompatibility complex (MHC) peptide-presenting molecules on their cell surfaces, along with a series of costimulatory molecules (Banchereau and Steinman (1998) Nature 392:245-252). Naïve T cells express receptors for these DC ligands. Following recognition of peptide-antigen presented in the context of class I or class II molecules, the structure of the T cell membrane is reorganized, bringing together the elements of the T cell receptor with other cell-surface molecules, including the co-receptors CD4 or CD8 and the costimulatory receptors CD28 and CTLA-4 (Monks et al. (1998) Nature 395:82-86; and Wulfing and Davis (1998) Science 282:2266-2269). Interactions within the newly formed macromolecular complexes determine the outcome of inductive events transduced into T cells by DC.
DC reside in a variety of tissues and display distinct tissue-associated phenotypes (Strunk et al. (1997) J. Exp. Med. 185:1131-1136; Caux et al. (1996) J. Exp. Med. 184:695-706; Wu et al. (1996) J. Exp. Med. 184:903-911; and Vremec et al. (1992) J. Exp. Med. 176:47-58). The relationships among the cell lineages of these different subsets of cells are not firmly established. A large body of work has emerged focusing on DC generated in vitro from bone marrow or blood precursors (Mayordomo et al. (1995) Nat. Med. 1:1297-1302; Nonacs et al. (1992) J. Exp. Med. 176:519-529; Steinman and Witmer (1978) Proc. Natl. Acad. Sci. USA 75:5132-5136; and Young and Steinman (1990) J. Exp. Med. 171:1315-1332). The cells generated in vitro express high levels of class I antigens and the series of costimulatory ligands associated with endogenous DC (Fagnoni et al. (1995) Immunology 85:467-474; and Banchereau et al. (2000) Annu. Rev. Immunol. 18:767-811). Importantly, they are able to efficiently activate naïve T cells, a function that is the signature of the DC.
Asthma is primarily a chronic inflammatory disease of the airways. This primary inflammation causes two secondary symptoms: (a) overly reactive bronchi that are more sensitive to various asthma triggers such as allergens, cold and dry air, smoke and viruses, and (b) airflow obstruction (i.e., difficulty moving air in and out of the lungs). These symptoms are typically manifested by coughing, wheezing, shortness of breath or rapid breathing, and chest tightness.
Allergic asthma is the most common form of asthma. Many of the symptoms of allergic and non-allergic asthma are the same. Allergic asthma is triggered by inhaling allergens such as dust mites, pet dander, pollens, or mold. Through a complex reaction, these allergens then cause the passages in the airways of the lungs to become inflamed and swollen, resulting in asthma symptoms.
Allergic asthma is characterized by pulmonary inflammatory infiltration and hyperreactivity to variety of lung irritants and stimuli such as methacholine. The hallmark of allergic asthma is abnormal expansion of Th2 cells in the lungs (Wills-Karp (1999) Annu. Rev. Immunol. 17:255-281; and Ray and Cohn (1999) J. Clin. Invest. 104:985-993). DC act as the major antigen presenting cells to naïve T cells in lymphoid organs (Steinman (1991) Annu. Rev. Immunol. 9:271-296). DC are present in the respiratory tract, and upon isolation from the trachea, bronchi, alveoli and visceral pleura, they are capable of antigen presentation to T cells (Holt and Schon-Hegrad (1987) Immunol. 62:349-356; and Sertl et al. (1986) J. Exp. Med. 163:436-451). In addition, it has been demonstrated using an ovalbumin (OVA) model of allergic asthma that pulmonary DC prime T cells, inducing a Th2 phenotype. Treatment of mice with GM-CSF modulated this effect toward a Th1 polarity, with an accompanying increase in message for IL-12 (Stumbles et al. (1998) J. Exp. Med. 188:2019-2031).